This week, he pledged a $50,000 reward to anyone with information that led to "establishing the whereabouts or what has happened to" his father.

"Whether in fact my father has met with foul play or suicide, we're asking anyone who may know something to come forward and any information which leads to the discovery of remains that can be forensically supported as my father's, my family are willing to reward that individual for that information with $50,000," he said.

"It's certainly something our family would have to focus on remortgaging houses and the like.

"And even though it may not seem huge or significant by societal standards on rewards for solving a case, it's certainly as much as our family is able to do for information that may lead to solving the disappearance of my father."

Mr Isles filed an affidavit to the Brisbane District Court on October 1 asking for the court to set aside the coroner's finding.

He argued Senior Sergeant Isles' mental condition had actually been improving after a decline during a Crime and Corruption investigation into his father that he said was tainted by "corruption" and a "closed and self-protecting police culture", which he was eventually cleared by.

A note was found after the Ayr police officer's disappearance, he was seen taking what was believed to be his shotgun from his home on the morning he disappeared and ammunition was found in the boot of his car.

"This is nobody's fault but mine. I feel old and have lost the will to do anything. I feel a failure and a loser, particularly to my family whom I love so much," the note read.

But Mr Isles said the undated note could have been written at any time and the gun didn't work.

"My father had seen through some of his darkest moments and no doubt during some of the deepest depths of desperation, considered taking his own life," his affidavit states.

The appeal was heard in the Brisbane District Court on November 16, where Judge Douglas McGill reserved his judgment.